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Sept. 10, 1963 J. w. GRAHAM ELECTROLYTIC GRINDING 2 Sheets-Shut 1 Filed April 8, 195a ux ubavuuaubll Sept. 10, 1963 J. w. GRAHAM ELECTROLYTIC GRINDING 2 Sheets-Sheet 2 Filed April 8, 1958 United States Patent 3,103,482 ELECTROLYTIC GRINDING John W. Graham, Koegasbrug, Republic of SoutlrAfrlca, assiguor, by mesne assignments, to Anocut Engineering Company, a corporation of Illinois Filed Apr. 8, 1958, Ser. No. 727,519 Claims. (Cl. 204-217) This invention relates to electrolytic grinding of the kind in which material is removed from a conducting workpiece by electrolytic means, the workpiece being held in close contact with a grinding electrode which has insulating spacers projecting from its working surface. In known processes of the kind in question the control of the working current is the critical factor. Elaborate precautions have to be taken to prevent excessive sparking or even arcing between the workpiece and the electrode. For this purpose very complicated and expensive control circuits have been devised.

An object of the invention is to provide an electrolytic grinding process and apparatus in which the current need not be controlled within very fine limits.

In a process according to the invention the zone of contact between the workpiece and the electrode is constantly submerged in electrolyte. The pool of electrolyte serves to quench any tendency to spark and are. Once the working current has been set at a predetermined mean value quite large variations above the mean do not lead to excessive sparking or arcing.

A simple way to carry out the process is to submerge the grinding electrode in a bath of electrolyte. The drawback here is that a large volume of electrolyte is required and that gland and insulating structure has to be provided for the shaft of the rotating electrode. Even so, the extra cost of electrolyte and the structure may be less than that of the latest current control devices. Total submergence at first glance appears to be the only way of conducting peripheral grinding with the process of the invention.

It is, however, possible to have a peripheral grinding electrode rotate in a slot in a trough, the feed of electrolyte to the trough being maintained at the same rate as loss occurs through the small gap between the electrode and the slot. It should be noted that the workpiece has to be fed substantially vertically.

Side cutting electrodes may also be submerged with the grinding face horizontal. However, a better way is to have a circumferential ridge around the grinding face so that a pool of electrolyte is maintained on the face. With such an electrode the best results are obtained with the grinding face horizontal. However, the face may be vertical in which case grinding should be concentrated towards the edge.

The most economical process according to the invention is with an annular electrode the inner surface of the electrode constituting the grinding surface and formations such as projection ridges and perhaps the rear wall of the tool constraining the electrolyte in the axial direction of the tool. Thus a pool of electrolyte is maintained on the grinding surface by centrifugal action.

The annular electrode is particularly suitable for form grinding and for grinding chisel shapes. In the latter case the groove complemented to the chisel shape serves to hold the pool of electrolyte.

Several embodiments of the invention are described hereunder and illustrated in the accompanying drawings, in which- FIGURE 1 is a schematic view in side elevation of apparatus according to the invention,

FIGURE 2 is a plan view of part of FIGURE 1,

3,103,482 Patented Sept. 10, 1963 FIGURE 3 is a vertical section through further apparatus according to the invention,

FIGURE 4 is an elevation of a modification of the embodiment of FIGURE 3,

FIGURE 5 is a horizontal sectional plan of a preferred embodiment,

FIGURE 6 is a horizontal sectional plan of apparatus adapted for chisel grinding,

FIGURE 7 is a horizontal fragmentary sectional view of a further modification, and

FIGURE 8 is a view similar to FIGURE 7 of another embodiment.

The apparatus shown in FIGURES l and 2 consists in a peripheral grinding electrode 7 with the usual insulating spacers such as diamond particles on its periphery. Above the electrode 7 is a trough 8 which has a slot 9 in its floor. The slot is partly covered by cover plates 10 which leave only a portion 11 of the electrode 7 exposed. The portion 11 is kept as small as is practicable and the gaps 12 between the plates 10 and the electrode 7 is kept as small as possible.

Electrolyte from a reservoir 13 is fed to the trough 8 through valves 14 and 15. The valve 14 is a shut off valve and the valve 15 is an adjusting valve which is so adjusted that the flow of liquid to the trough is equal to the loss of liquid through the gaps 12 when the electrode is running. It is also possible to have the inflow to the trough float controlled. In any event the object is to keep a constant level 16 of liquid in the trough 8 and to keep the portion 11 constantly submerged in electrolyte.

The electrolyte is collected below the trough 8 and passed through the usual filtering and settling apparatus 17 and pumped back to the reservoir 13. If only intermittent operation takes place the pump need not replace liquid in the reservoir at the same rate as it flows from the reservoir. When the apparatus is not used the valve 14 is closed to conserve electrolyte.

It is not likely that the apparatus of FIGURES l and 2 will find wide application as the through-put of electrolyte is considerable and hence extra power is required to operate the pump.

In FIGURE 3 a more economical apparatus is illustrated. Here a side grinding electrode 21 with its working face horizontal is shown with a ridge 22 around its periphery. Electrolyte is fed to the centre of the electrode 21 and the ridge 22 keeps a constant pool of electrolyte on the grinding face. Electrolyte leaving the face is caught in a launder 23.

In both the embodiments of FIGURES l and 2 and FIGURE 3 the workpiece 19 has to be fed vertically. In many cases this is a disadvantage.

If the electrode of FIGURE 3 is inverted as in FIG- URE 4 an ordinary side cutting grinder is simulated. In this case the pool of electrolyte is concentrated towards the edge of the electrode and grinding must of necessity be confined to that region. Furthermore, elaborate precautions to prevent splash are necessary.

A preferred form of electrode is shown in FIGURE 5. Here an annular electrode 33 with a flange 34 for securing to a drive shaft 35 has insulated spacers on its inner surface. An inwardly projecting ridge 36 acts as a weir to electrolyte confined to the grinding surface by centrifugal force. The rate of feed of electrolyte need not be more than in conventional processes but nevertheless complete submergence of the working zone is maintained.

In FIGURE 6 a modification of the embodiment of FIGURE 5 is shown in detail. In this case the electrode is adapted to grind a chisel-shaped rock-drill with an inserted tungsten carbide cutting formation. The electrode 33 is grooved at 42 complementally to the ultimate chisel shape. While the chisel shape is symmetrical, the groove 2 is displaced relatively to the transverse plane of the 3 electrode to enable the stem 41 of the rock drill to be clamped by an arrangement which is not pertinent to the present invention.

As in the embodiment of FIGURE 5, electrolyte is contained in the groove 42 to ensure complete submergence of the working zone.

By the use of a profiled groove it is possible to erode almost any shape into a workpiece. Where workpieces are adapted to be chucked inside the bore of an annular electrode the profile may be formed transverse to the plane of the electrode as shown in FIGURE 7. Otherwise the profile has to be tilted like the groove 42 in FIGURE 6 as shown in FIGURE 8. In the latter case it is essential that the outer rim of the groove must project radially inwardly as far as the highest peak on the profile in the electrode or else a ridge 45 must be provided to ensure retention of a pool of electrolye.

In all the above applications of the electrolytic grinding process it is advisable to shield such parts of the workpiece as not to be eroded with an insulating coating and also parts of the electrode itself.

I claim:

1. In apparatus for electrolytic shaping of a conductive workpiece, an annular electrode having a conductive working face on its inner surface adapted to carry a liquid electrolyte, insulating spacing means projecting above said working face a small spacing distance and against which the workpiece is adapted to be held, means connected to said electrode for rotating the latter, means for supplying liquid electrolyte t the working face of the electrode at a rate sulficient to flood the area of contact between the workpiece and the spacing means, and lip means on the electrode being so shaped as to constrain electrolyte from flow in the axial direction of the electrode.

2. In grinding apparatus of the type in which a con ductive workpiece and a rotatable electrode carrying insulating spacers on its working face are brought into close proximity with the workpiece contacting the spacers, including means for continuously introducing electrolyte between the electrode and the workpiece in the area of contact of the workpiece with the spacers, means for applying a direct current potential across the electrode and workpiece in a sense to make the workpiece an anode for the electrolytic removal of material from the workpiece, the combination with the electrode of bafiie 4 structure partially restraining the flow of electrolyte from the electrode in the axial direction and causing flooding in the area of the workpiece and electrode spacer contact for inhibiting sparking and arcing.

3. Grinding apparatus of the type claimed in claim 2, including means controlling the flow of electrolyte to the electrode and workpiece at a minimum rate in the order of the loss therefrom.

4. The apparatus claimed in claim 1 in which the electrode is shaped with projections defining a groove in the annulus.

5. The apparatus claimed in claim 4 in which the electrode has a groove complemental to a chisel shape the walls of the groove constraining the electrolyte.

6. The apparatus claimed in claim 5 in which the groove is inclined in section to planes transverse to the annulus to allow for the shaping of long-stemmed articles.

7. An electrode for the electrolytic shaping of a conductive workpiece comprising an annulus adapted to carry a liquid electrolyte, insulating spacers on the inside surface of the annulus, and lip means to constrain liquid flung against the inside surface on rotation of the annulus in an axial direction.

8. The electrode claimed in claim 7 having at least one groove on the inside surface of the annulus.

9. The electrode claimed in claim 8 having one V- shaped groove.

10. The electrode claimed in claim 9 in which in section the V is symmetrical about itself and its axis of symmetry is inclined to planes at right angles to the axis of the annulus.

References Cited in the file of this patent UNITED STATES PATENTS 2,385,198 Engle Sept. 18, 1945 2,764,543 Comstock et a1 Sept. 25, 1956 2,798,846 Comstock July 9, 1957 2,805,197 Thibault Sept. 3, 1957 2,826,540 Keelen'c Mar. 11, 1958 2,934,631 Imalis et al Apr. 26, 1960 2,939,825 Faust June 7, 1960 OTHER REFERENCES Pirani et al.: Zeitschrift fur Metalkunde, volume 16, pages 132-33, April 1924. 

1. IN APPARATUS FOR ELECTROLYTIC SHAPING OF A CONDUCTIVE WORKPIECE, AN ANNULAR ELECTRODE HAVING A CONDUCTIVE WORKING FACE ON ITS INNER SURFACE ADAPTED TO CARRY A LIQUID ELECTROLYTE, INSULATING SPACING MEANS PROJECTING ABOVE SAID WORKING FACE A SMALL SPACING DISTANCE AND AGAINST WHICH THE WORKPIECE IS ADAPED TO BE HELD, MEANS CONNECTED TO SAID ELECTRODE FOR ROTATING THE LATTER, MEANS FOR SUPPLYING LIQUID ELECTROLYTE TO THE WORKING FACE OF THE ELECTRODE AT A RATE SUFFICIENT TO FLOOD THE AREA OF CONTACT BETWEEN THE WORKPIECE AND THE SPACING MEANS, AND LIP MEANS ON THE ELECTRODE BEING SO SHAPED AS TO CONSTRAIN 